The Bluetooth baseband technology supports two link types: a synchronous connection oriented (SCO) type (used primarily for voice) and an asynchronous connectionless (ACL) type (used primarily for packet data).

Different master-slave pairs of the same Piconet can use different link types and the link type may change arbitrarily during a session. Each link type supports up to sixteen different packet types. Four of these are control packets and are common for both SCO and ACL links.Both link types use a time division duplex (TDD) scheme for full-duplex transmission.

The SCO link is symmetric and typically supports time-bounded voice traffic. SCO packets are transmitted over reserved intervals. Once the connection is established, both master and slave units may send SCO packets without being polled.The SCO link type supports circuit-switched, point-to-point connections and is used often for voice traffic. The data rate for SCO links is 64 kbps.

The ACL link is packet oriented and supports both symmetric and asymmetric traffic. The master unit controls the link bandwidth and decides how much Piconet bandwidth is given to each slave, and the symmetry of the traffic. Slaves must be polled before they can transmit data.

The ACL link also supports broadcast messages from the master to all slaves in the Piconet. Multi slot packets can be used in ACL and they can reach maximum data rates of 721 bps in one direction and 57.6 kbps in the other direction if no error correction is used.

Data packets are protected by an automatic retransmission query (ARQ) scheme. Thus, when a packet arrives, a check is performed on it. If there is an error detected, the receiving unit indicates this in the return packet. In this way, retransmission is done only for the faulty packets. Retransmission is not feasible for voice so better error protection is used.

The Bluetooth baseband technology supports two link types: a synchronous connection oriented (SCO) type (used primarily for voice) and an asynchronous connectionless (ACL) type (used primarily for packet data).

SDP (Service Discovery Protocol)

1.it discovers which services are available

1. It Identifies the characteristics of the services

2. It uses a request/response model where each transaction consists of one request protocol data unit (PDU) and one response PDU

3. SDP is used with L2CAP

4. It is optimized for the dynamic nature of bluetooth

6.SDP does not define methods for accessing services.

Asynchronous Connection-Less (ACL)

1. Designed for data traffic

2. Packet switched connection where data is exchanged sporadically as and when data is available from higher up the stack

3. Data integrity is checked through error checking and retransmission

4. One ACL link between a master and a slave

Synchronous Connection Oriented (SCO)

1. Intended for use with time-bounded information such as audio or video.

2. Provides a circuit-switched connection where data is regularly exchanged.

3. Retransmission is not necessary, since data is real-time.